Nanoelectronic devices with length scales below 100 nm are of great interest for the functional semiconductor field. Theoretically, making devices with characteristic length scales less than 10 nm is possible, but it takes a long time, is hard to control, and is expensive. Existing methods for fabricating devices below 100 nm include both top down and bottom up approaches.
Conventional top down approaches using photolithography or electron beam lithography require utilization of photoresists for selective formation of desired materials into functional devices. Because of proximity effects, photolithography is limited in the resolution achievable. Because of the minimum energy required for photoresist reaction energy, electron beam lithography is limited in the speed obtainable.
Direct-write top down approaches have included atomic force microscopy (AFM), direct writing of liquids, i.e., dip pen nanolithography, and scanning tunneling microscopy (STM) writing of oxides and charge replicas. These methods suffer from slow speeds, lack of a general set of building materials for fabricating electronic components, and a constraint to two-dimensional structures.
Existing tools for creating three-dimensional structures employ, for example, electron beam and ion beam decomposition of chemical vapor precursors. Such tools have been useful in mask and chip repair and have been shown to be capable of writing three-dimensional structures. Typically, organometallic precursor gases adsorbed onto substrate surfaces are decomposed using energy supplied from incident beams, depositing the desired metal or insulator. This technique facilitates deposition of nanometer- to micrometer-size structures with nanometer precision in three dimensions, without supplementary process steps such as lift-off or etching procedures. Although successful in creating high resolution three-dimensional structures, both scanning electron microscopy (SEM) and focused ion beam (FIB) chemical vapor deposition (CVD) suffer from significant contamination by the organic components of precursor gases. Carbon contamination from typical precursor gases may exceed 50%, thus altering device conductivities to levels unacceptable for many desired applications. Device fabrication by energetic-beam CVD is also constrained by an inherently small number of available precursor gases, thus limiting the variety of materials that can be deposited. Finally, because existing processes are serial and sufficient beam energy must be applied to decompose the precursor, deposition speeds are very slow.
In typical currently-employed bottom up approaches, layers are selectively applied to, rather than removed from, a substrate. For example, nano-scaled building blocks synthesized precisely by chemistry or other methods may later be assembled by, e.g., self assembly. Presently, the complexity of logic that may be built in this way is extremely limited.
In contrast, nature is excellent at predicated assembly of complex molecules such as DNA on a scale similar to that of present-day nanostructures. Nature can make precise molecules with enzymes such as polymerase that typically have extremely low error rates by utilizing feedback and performing error correction. Direct feedback and error correction are seldom implemented in present fabrication processes, and hence the yield of functional devices is low in comparison to functional molecules formed by biological processes.
What has been needed, therefore, is a system for fabrication of two- and three-dimensional functional structures with a characteristic length scale below 100 nm that employs a precise and rapid patterning of high purity nanoscale building blocks.